I disagree. I think the "us vs them" mentality will exist in many people, and sports fanaticism creates a harmless outlet for it. If we deprive the "us vs them" minded people of harmless outlets like team sports, they may instead focus their attention on political or ethnic teams.
If there is any substitution affect at all, I suspect sports fanaticism is highly beneficial - compare the damage done by rampaging celtics fans to the damage done by rampaging communism fans or rampaging hutu fans.
An "outlet" is one of those Freudian concepts that hasn't been proven and Wikipedia says that scientific opinion is divided.
It just seems illogical to me.
When your options for spending time and energy are infinite, are we required to include a certain number of angry activities to expend anger? A certain number of negative activities to expend negativity? Then why should it be necessary to have a certain number of "us vs them" activities?
If there is any substitution affect at all, I suspect sports fanaticism is highly beneficial - compare the damage done by rampaging celtics fans to the damage done by rampaging communism fans or rampaging hutu fans.